1. Field of the Invention
The present invention relates to a degradable container, and particularly relates to the container which comprises a thermoplastic polymer composition, has degradability in the natural environment, and is excellent in transparency and impact strength.
2. Related Art of the Invention
Plastic containers have been conventionally prepared from polyethylene, polyethylene terephthalate, polyvinyl chloride, polypropylene and other resins.
Although some of these containers prepared from these resins are excellent in transparency, these containers have a very slow rate of degradation and thus remain semipermanently when discarded as refuse and buried under the ground. Disposal of these containers in the ocean causes aesthtic damage or destruction of the living environment of marine organisms.
Containers of a polyhydroxy butyrate/polyhydroxy valerate copolymer have also been developed, and these are effective for degradability. However, these containers are insufficient in transparency and have a disadvantage that the contents cannot be identified.
On the other hand, polylactic acids and copolymers of lactic acid and other hydroxycarboxylic acids (generic name of the polylactic acid and the copolymer will hereinafter be referred to simply as a lactic acid based polymer) have been developed as thermoplastic polymers having degradability. These polymers can be completely biodegraded within a few months to an year in an animal body. When the polymers are placed in soil or sea water, they start to decompose within a few weeks in a moist environment and disappear within several years. Further, final degradation products of these polymers are lactic acid, carbon dioxide and water which are nontoxic to humans.
No prior art on manufacturing a transparent container with the lactic acid base polymer is known.
That is, on processing the lactic acid based polymer by known molding methods such as compression molding, and injection molding the polymer cannot provide containers having sufficient impact strength for practical use as transparent containers and causes the problem of impaired transparency when improved impact strength is sought. Consequently, containers having both transparency and impact strength which is satisfactory for practical use have not yet been obtained.